1. Field of the Invention
This invention relates to magnetic recording and reproducing apparatus, particularly to video reproducers of the helical scanning type in which a magnetic record/playback head is operatively supported within a rotating drum for scanning a magnetic tape along a plurality of adjacent discrete tracks oriented at an angle relative to the lengthwise direction of the tape, and in which special head positioning assemblies are provided to enable repositioning of the head to enable accurate track following.
2. Description of the Prior Art
Helical scan video tape recorders embodying automatic track following features to compensate for non-uniform tape motion, tape stretching, and the like are becoming well known. Such recorders are, for example, disclosed in U.S. Pat. Nos. 4,143,405 (Kubota) and in 4,151,570 (Ravizza)
In addition to such patents wherein track following systems in general are disclosed, it is also becoming known to provide various types of assemblies for enabling a playback head mounted within a rotary scanning drum to be positioned transversely to the path of a magnetic recording medium disposed helically about the drum to enable the head to be moved transversely, thereby enabling automatic track following. For example, in U.S. Pat. No. 4,151,569 (Hathaway) two general types of head positioning assemblies are depicted. The first type utilizes a piezoelectric bender element, while the second type, generally depicted in FIG. 10 of that patent, is based on the use of a leaf formed of magnetically permeable material which is arranged to pivot from a stable support within the drum, rather than bend as provided in the piezoelectric embodiment there depicted. Also mounted on the drum and on both sides of the magnetically permeable leaf are a pair of electro-magnets for producing a magnetic field through the leaf and which, when energized, cause the leaf to deflect, thereby moving the head in the desired transverse direction.
Head positioning systems utilizing piezoelectric reed constructions as the transducer for moving the head are known to be subject to variations due to aging and stress, and are therfore not particularly desirable. While the second embodiment depicted in the above-noted patent, based on the use of a magnetically permeable member, avoids certain problems common to piezoelectric problems, that technique is lacking in practicality in that the need for a pivoting member and dual drive coils contributes to head misalignment and azimuth problems.